I have been interested in finding a direct means fox prospecting far oil for some time, although I have spent my entire career of nearly a half century in geophysical prospecting for oil, including the most widely used methods of seismic prospecting for oil. All geophysical is methods including the must used seismic reflection method have been indirect, i.e., aiming at finding structures, stratigraphic traps, or inferring lithological characteristics only. The chance of finding oil for the seismic techniques is about one in six to seven. In the present invention, the chance of finding oil will be about one in two to three.
The electromagnetic (EM) wave propagation depends primarily an the electric permittivity of the earth materials of rocks, while the conductivity of these earth materials is very low and the magnetic permeability is virtually constant. How the dynamic electromagnetic wave methods of this provisional application differ from any other methods lies in the fact using the physical properties of the oil itself in contrast to surrounding rocks of geological formations, gas, and water. Oil has an extremely low electric permittivity or dielectric constant, which is about 4 with an electromagnetic wave velocity of 50 m/us while fresh or salt water has a value of permittivity 81 with an electromagnetic wave velocity of 33 m/us. Surrounding sediments, usually say limestone, which has a value of permittivity 7-16 with an electromagnetic wave velocity of 75-113 m/us and that for sandstone 5-15 with an electromagnetic wave velocity of 77-134 m/us. It is these ideal electric permittivity contrasts that provide a means to use dynamic electromagnetic method for direct prospecting for oil.
The present invention relates to direct prospecting for oil in any environment worldwide at various depths. Using an extremely broad band of electromagnetic waves, this electromagnetic wave prospecting method should penetrate various depths which could be comparable to the penetration of seismic waves. Most importantly it would provide a means to directly identifying where the oil is and find the interfaces between the water and oil, as the permittivity of the water is 81 with an electromagnetic wave velocity 300 m/us.
During the last two decades, ground penetrating radar has been employed in shallow depth ranging from the surface to about 50 to 100 meters, which are operated in the radar frequency ranges of 50 to 1,000 mHz solely based on antenna source and antenna receivers.
This patent application is solely for prospecting for oil directly using frequency range from as low as DC to radar frequency, covering from the surface to a depth of greater than 3,000 meters or more for deep seated oil deposits. The art of achieving such a depth penetration must rely upon the design of the sources as well as the receivers, which will be expounded in the following section.
The essential part of this patent application is divided into two designing sections of the source and receiver, and one section on practice in the field.
1. The Source
In order to have the electromagnetic waves to penetrate to a depth of 3,000 m or more, a very low-frequency in the radio LF to UHF frequency range type of electromagnetic source is required, which would have the capability of delivering the power in the range of at least 10 to 100 kw or more with a voltage of 1,000 volts or more and a current of 10 to 100 Amperes or more.
1.) Pulse Excitation
An electric pulse of 1-ms pulse width or wider pulse width so that the one-sided positive excitation of the source arid one-sided negative excitation can be used as shown in FIG. 1a. The first derivatives of these two pulses are the Gaussian functions as shown in FIG. 1b. The second derivatives are the typical wave forms of one peak and one trough shown in FIG. 1c. The Gaussian-function source in the form of (a/), xc2xd exp [-a(t-to)2], where the time is so chosen such that the function normalized by its peak value is nearly zero shown to FIG. 2a the pulse width of which is defined as w=4 o where o=(2a) xc2xd is the standard deviation of the Gaussian-pulse, which represents the decay time of the electric current; their amplitude spectrum is also a Gaussian which is in the form of exp(-2f2/a), where f is the frequency in Hz and fc is the cut-off-frequency as shown an FIG. 2b is defined here as the frequency at which the amplitude has decayed to e-1 or 0.3679 times the peak value. All the derivative sources are continuous.
The return reflections at the depth of 3,000 m or deeper reach the surface by only the one-sided positive excitation and would be approximately 60 us or 30 us each way or longer, i.e., downward and upward of the pulse, before the one-sided negative pulse excites the source mechanism, which will be described in the sequel.
2.) Chirping or Sweeping Source:
Another source excitation can be easily achieved by means of a chirping or sweeping frequencies. The sweeping- frequency source can be from the low to high frequency or from the high to the low frequency. The near-vertical reflections from the depth can be processed by means of correlation techniques.
Frequency range would be from 0.10 to 100 mHz, corresponding to the wavelength fox a high-end average limestone velocity of 100 m/us from 1,000 m to 1 m. Despite the radio LF frequency, the high contrast of the impedance at the oil/salt water interface would produce a strong reflection.
Apparatus
Now the invention of the apparatus of the source and receiver is described in the following;
1.) The Source Apparatus
The source apparatus consists of an electromagnetic pulse, impulsive or chirping, generated multi-turn coil, which would in turn generate magnetic field the capacity to produce the power, in turn, the field will be directed by a parabolic directional reflector into the earth as shown in FIG. 3. The source multi-turn-coil/parabolic-reflector does not need to be limited to only single one source but it could be a multi-source consisting of a number of multi-turn-coil/parabolic-reflectors which could be steered to give a boon-forming synchronization.
A current is introduced to the mild-turn coil, where the terminal of the incoming current is designated as positive and the terminal of the outgoing current is designated as the negative, there is an applied voltage across these two terminals. For the present application, the voltage will be about 1,000 volts or more and the current be between 10 to 100 Amperes or more to provide adequate power for electromagnetic wave propagation into a greater depth in the earth. The present source is geometrically symmetrical with respect to the center of the well and the vortex of the parabolic reflector.
2.) The Receiver Apparatus
The receiver apparatus consists of a multi-channel data acquisition system. Each channel is equipped by a directional impedance-matched antenna, which is capable of receiving wide-band electromagnetic signals. Receivers are formed in a variety of patterns with respect to the location of the source(s), namely a linear or areal coverage, or a radial coverage.
The number of channels depends on the subsurface coverage for the electromagnetic imagery. Normally, at least a 48 or 96 channels are required for such an electron wave reflection prospecting for oil directly.
The present invention fundamentally differs from any prior-art patents to be cited below owing to the fact that I discovered first the fact that the propagating part of the electromagnetic wave primarily depends on the electric permittivity of the medium which for the oil is extremely low. The interface between the geological formation including sedimentary rocks, namely, sandstone, shale, limestone, and any other rocks as a upper medium, and the sedimentary rocks containing oil as a lower medium provides strong reflection and refraction of electromagnetic waves. Upon this discovery, I then searched in vain to find the prior art inventions as available or patented. I was forced to invent on my own an apparatus and system explicitly for direct-finding oil in all the depth of the oil desposits to be elaborated in the sequel.
With the basic operation of the system having been described above, let us now discuss the underlying phenomena involved which enables this system to be directly find oil. The system of the present invention uses a transient time-domain electromagnetic pulse, a sweep-frequencies, from low to high, from high to low, and a predesignated time domain electromagnetic waves as an excitation source.
The technique utilized in the system of the present invention has been designated by the inventors as xe2x80x9cTrue Electromagnetic Waves.xe2x80x9d (abbreviated to TEMW as TM). The propagation of a transient time-domain pulse, a sweep of frequencies or a predesignated electromagnetic wave train is fundamentally a dynamic electromagnetic phenomenon. It is completely governed by the electromagnetic wave equations, which are derived from Maxwell""s Equations, upon which the present invention is based. Details of the fundamentals of the transient electromagnetic waves are referred to an earlier patent application Ser. No. 08/807,645, filed on Feb. 27, 1997.
In the method of the present invention, the prospecting for oil is done directly by ascertaining presence of oil in the earth, where there are upper, non-oil bearing geological formations which are in contact with an oil bearing geological formation immediately below to form a distinct non-oil/oil interface.
More specifically, the method comprises transmitting an electromagnetic wave or waves downwardly through the first formations to said interface, with the wave or waves being reflected and/or refracted upwardly from the interface as reflected and/or refracted wave or waves.
These reflected and/or refracted wave or waves are received at a receiving location or locations, with the reflected and/or refracted wave or waves having a reflected and/or refracted waveform or waveforms that would directly indicate the presence of oil.
The reflected and/or refracted wave form or forms are analyzed to ascertain a presence of a wave characteristic or characteristics found in a reflected and/or refracted wave or waves that are reflected and/or refracted from a non-oil/oil bearing interface.
In the advent of fundamental understanding of the time-domain electromagnetic wave propagation and rapid processes in technology made in the petroleum industry mainly during the last half century, the present invention is the culmination of the true time-domain electromagnetic waves embodying all the frequencies according to the spectrum of the dynamic transient time-domain electromagnetic waves as excited at the source. Some of the previous patents are dated back to more than a half century ago. The inventors even then reflected the inventive farsightedness but after all did not have the predictive insight to the future and stayed solely in the frequency-domain.
The patents of which possess a different degree of relevant prior-art relevance of the present patent application are eleven as follows. We shall examine these patents in a chronologically reversed order:
1. U.S. Pat. No. 5,147,753 (Etten and Brown, 1994) dealt primarily with the instrumentation of an earth probing system and uses deep penetration of electromagnetic waves into soil and other media. Advantage was taken of the low attenuation of radar waves in soil by frequencies of above three megahertz or less.
2. U.S. Pat. No. 4,504,833 (Burke was related to pulse radar detection of targets and extended media, including natural phenomena such as oil, coal and oil deposits within the earth.
3. U.S. Pat. 4,504,813 (Fowler et al., 1985) was related to a synthetic pulse radar for detecting geophysical phenomena generically.
4. U.S. Pat. No. 4,245,191 (Schroeder, 1981) dealt with a transmitter and a receiver in the frequency domain with an unmodulated carrier of selected wave length into the ground for detecting inclusions in subsoil only.
5. U.S. Pat. No. 3,806,795 (Morey, 1974) was essentially the pre-generation of ground penetrating radar system now nearly developed commercially for a very shallow depth of 8 to 10 feet.
6. U.S. Pat. No. 2,953,742 (Herbold et al, 1960) comprised mainly a generator, a capacitor, And adjustable spark gap terminals. The latter was used there between arranged to discharge the said capacitor into the antenna and generate an electromagnetic wave front into the shallow depth of the earth.
7. U.S. Pat. No. 2,766,422 (Carbonetto, 1956) intended to generate a modulated carrier wave by a high frequency carrier wave to be modulated with a relatively low-frequency wave in the frequency-domain. The radiation of the modulated carrier wave then was used as the source for penetrating the ground and to observe the radiation f the reflected wave.
8. U.S. Pat. No. 2,426,918 (Barret, 1947) addressed electric prospecting in the frequency-domain of mapping the near surface subsurface zones by means of varying the frequency of the incident wave and observing the reflected wave.
9. U.S. Pat. No. 2,268,106 (Blau, 1941) dealt with utilizing commercial broadcasting stations and receiving dealt with radio waves or electromagnetic waves of radio frequencies.
10. U.S. Pat. No. 2,139,460 (Potapenko, 1938) was based upon the inventor""s discovery of that crude oil has a selective absorption for electromagnetic radiation corresponding to the part of its spectrum of short and ultraviolet radio waves. The patent dealt with two specific different frequencies.
11. U.S. Pat. No. 2,077,707 (Melton, 1937) dealt with an improvement in electrical prospecting shallow subsurface prospecting to determine the character and location of shallow geological formations mentioning reflection and refraction impulses.
12. U.S. Pat. No. 1,818,331 (Jakosy, 1931) dealt with electrical inductive methods only for prospecting electrically conductive underground ore bodies.
None of the patents which have been searched addressed the fact of the electric permittivity of oil is extremely low at about 4 in comparison with other that of any of the geological media as well as water and gas. The interface of any known geological media including shale, sandstone, limestone, siltstone, mudstone, etc. with the oil provided a means of strong reflections of electromagnetic waves for the near vertical reflection method and of strong refractions for the wider-angle refraction method. The discovery of this very fact is the essence of the present invention for direct finding oil. The depth to which the present invention hereby referred extends from a shallow depth of 1,000 to 5,000 feet to an optimal depth of 10,000, 15,000 feet or greater at which most of the known oil deposits were found (see figures attached).